Impact modified thermoplastic compositions of polycarbonate (PC) combined with polyester resins have been disclosed. For example, in Liu, U.S. Pat. No. 4,536,538, impact-modified polycarbonate compositions comprising an impact modifier of poly(cyclohexanedimethylene iso- and terephthalate) and an olefin-acrylate copolymeric resin, e.g., ethylene ethyl acrylate are disclosed. The compositions of patent '538 are said to have increased thick section impact in comparison to polycarbonate alone. In European Patent Application 132339 (published Jan. 30, 1985), there are disclosed thermoplastic resin compositions comprising pigmented polyester, e.g., poly (1,4-butylene terephthalate) resins (PBT), and/or aromatic polycarbonate resins having a multi-stage polymeric impact-modifier of styrenic monomer, crosslinking monomer and optionally, non-styrenic non-crosslinking monomer. In Cohen et al., U.S. Pat. No. 4,257,937, thermoplastic PBT resin compositions are impact-modified by a combination of a polyacrylate resin, e.g., n-butyl acrylate and an aromatic polycarbonate, e.g., poly(bisphenol-A carbonate). In European Patent Application 33993 (published Mar. 13, 1985), are disclosed thermoplastic molding compositions comprised of PBT, an aromatic polycarbonate, e.g., poly(bisphenol-A carbonate) and a modifier combination comprising an acrylate/methacrylate core-shell graft copolymer resin and a polyolefin or an olefinic copolymer. In European Patent Application 107,048, are described thermoplastic blends of an aromatic polycarbonate, poly(ethylene terephthalate) (PET), and an acrylate-based rubbery core (meth)acrylate outer shell multi-stage polymer.
PC/polyester compositions have also been modified in order to improve their resistance to low temperature impacts. For example, in European Patent Application 79,477 (published May 25, 1983), and in Liu, U.S. Pat. No. 4,320,212, are disclosed modified thermoplastic polyester compositions which comprise PBT or a block PBT copolymer, optionally blended with PET and an impact modifying combination of a core-shell polymer having a rubbery conjugated dienic polymer core and a polymerized (meth)acrylate shell, optionally with an aromatic polycarbonate. The compositions of the '477 EPO Patent Application are described as having enhanced resistance to low temperature impact fracture, but still greater impact resistance at temperatures below -30.degree. C., and even at -51.degree. C. would be desirable.
It has now been unexpectedly discovered that thermoplastic compositions comprising polycarbonates and poly(cyclohexanedimethylene arylates) demonstrate excellent impact strength at low temperatures when modified by a multi-stage polymer having a rubbery core and an outer shell comprising polymerized (meth)acrylate. Moreover the impact strength levels attained have never before been seen with such low levels of rubber content in any known composition of the polyester type.